1. Field of the Invention
The present invention relates to a stage system for a lithographic apparatus, a lithographic apparatus including such stage system and to a method for manufacturing a device.
2. Description of the Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. including part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Conventional lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at once, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
US patent application 2005/0255624 describes a substrate stage of a lithographic apparatus. The substrate stage is driven by a motor to be movable in a plane. The motor includes a stationary coil which, when operated, creates a field to interact with magnets included in the substrate table to thereby generate a force acting on the substrate table. The stationary coil includes a plurality of stationary coil sections, to enable simultaneous independent driving of two stages. The coil sections are overlapping to enable the stages to be swapped. A position of each of the stages is measured by a plurality of interferometers.
Accuracy of the interferometer measurements are affected by thermal effects due to a heat generated by the coils. A measurement by an interferometer is based on a wavelength of an interferometer beam. The wavelength of the interferometer beam is dependent on a temperature of a medium through which the interferometer beam travels. The interferometer beams at least partly travel along a path over the stationary coil. Dissipation in the coil (or in sections thereof) by a powering of the motor to drive the stage, may therefore have an effect on a temperature along the path of the interferometer beam, thereby affecting a wavelength of the beam, and consequently an outcome of a determination of a position of the stage from an interferometer readout.